Solar cell modules including semiconductor wafers made of silicon or selenium is produced by, while degassing, heating under reduced pressure a laminated body obtained by laminating sealing materials for a solar cell onto the top and bottom surfaces of a solar cell element including wafers of a silicon semiconductor element or selenium semiconductor element with a function to generate an electric current by irradiation of light, the wafers having been connected directly or in parallel with an interconnector, and superposing a transparent top side protective material on the top surface of the sealing materials for a solar cell and a bottom side protective material on the bottom surface of the sealing materials for a solar cell, thereby integrally laminating the protective materials to the top and bottom surfaces of the solar cell element via the sealing material for a solar cell. Also in solar cells having a structure where a solar cell element made of silicon or a compound semiconductor has been laminated in a thin film form onto a substrate, sealing materials for a solar cell as described above have been used for sealing solar cell elements.
With respect to the sealing material for a solar cell to be used for such a solar cell module, for example, Patent Document 1 has proposed a protective sheet for a solar cell module, the protective sheet being made of an ethylene copolymer containing an organic peroxide, wherein the organic peroxide comprises a dialkyl peroxide (A) and at least one peroxide (B) selected from the group consisting of alkyl peroxyesters and peroxyketals are compounded as organic peroxides at a weight ratio (A)/(B) of 10/90 to 90/10.
The above-mentioned protective sheet for a solar cell module is formed from an ethylene copolymer and contains an organic peroxide in order to impart heat resistance; a solar cell module has been produced by superposing a protective sheet for a solar cell module onto a solar cell element, thereby forming a laminated sheet or a laminated body, and then vacuum laminating the laminated sheet or the laminated body to heat it while pressing it in its thickness direction, thereby decomposing the organic peroxide in the protective sheet for a solar cell module to cause crosslinking of the ethylene copolymer, thereby imparting heat resistance thereto and at the same time, integrating the solar cell element to the protective sheet of a solar cell module.
Accordingly, if the crosslinking in the protective sheet for a solar cell module is performed unevenly, the heat resistance of the protective sheet for a solar cell module will partially become insufficient and there will be caused a problem that the durability of a solar cell module to be obtained deteriorates.
In order to prevent the occurrence of such a problem, instead of heating, in a conveyance state, a laminated sheet or a laminated body with a protective sheet for a solar cell module being superposed onto a solar cell element, it is necessary to cut the laminated sheet or the laminated body into a desired shape beforehand, then temporarily bond the laminated sheet or the laminated body in several minutes or several tens of minutes in a stationary state under the application of pressure in the thickness direction using a vacuum laminator, and then carry out a crosslinking step of fully bonding them in several tens of minutes to one hour by heating them to a temperature as high as the organic peroxide can decompose, which have resulted in a problem that the production efficiency of a solar cell module is low.
Although the above-mentioned protective sheet for a solar cell module is crosslinked with organic peroxide in order to impart heat resistance, this causes a problem that it becomes impossible to produce a protective sheet for a solar cell module due to the occurrence of the decomposition of the organic peroxide during the production of the protective sheet for a solar cell module or the adhesive property of the protective sheet for a solar cell module decreases, or a problem that a decomposition product derived from the organic peroxide is formed in a adhesive interface, so that the adhesive property of the protective sheet for a solar cell module decreases.
In other words, since solar cell elements are precision components, there may be arisen a problem that gas derived from decomposition products of organic peroxides is generated from a protective sheet for a solar cell module during the production or use of a solar cell module, so that the cell performance of a solar cell deteriorates.